The present invention relates generally to printing apparatus, and particularly to ink-ejecting printing devices.
A print head includes an array of ink-ejecting nozzles. The print head scans, i.e., horizontally reciprocates, on a carriage across media and projects ink according to an intended image presentation, e.g., prints text or graphics across a page. A swath of image presentation across the page then lies along the print head swath path. The printer then advances the media past the print head swath path. By coordinating print head scanning, ink projection from the print head, and media advance, the printer deposits ink on the media in an appropriate pattern to generate the intended print image. A variety of methods of coordinating media advance and print head scanning have developed to efficiently deposit ink on the media. For example, some devices print in either direction, i.e., can print while the print head scans from right to left and can print while the print head scans from left to right.
Generally, the media advance distance equals the print head swath height. In other words, the print head lays down a pattern of ink across the page with a height or vertical distance, i.e., perpendicular to the scan direction, known as the xe2x80x9cswath height.xe2x80x9d By executing a scan and print maneuver across the page width, the printer deposits an ink pattern, i.e., image swath, with a vertical height corresponding to the swath height. Advancing the media by a distance equal to the swath height and between successive printing scans eventually exposes to the print head the entire vertical and horizontal dimensions of the media and gives opportunity for the print head to deposit ink on the entire media.
In some cases, however, the media advance does not equal the swath height. For example, the paper advance distance is less than the swath height when the device executes multiple passes relative to a given portion of the page. This is typical in photographic or high resolution/multi-color printing jobs where the print head requires one or more xe2x80x9cpassesxe2x80x9d over a given portion of the media. The media advance height may in some cases exceed the swath height. For example, when no printing is required the media advance can be significantly more than swath height. This action is also known as a xe2x80x9cwhite space skip.xe2x80x9d As used herein, term xe2x80x9cwhite spacexe2x80x9d or xe2x80x9cblank dataxe2x80x9d refers to a print head ejecting no ink and adding no image presentation to media thereunder.
Print heads are characterized by the number of ink-dispensing nozzles, printer resolution or xe2x80x9cdots per inchxe2x80x9d (dpi), and the swath height. Swath height is a function of the number of nozzles and the desired resolution. More particularly, swath height equals the number of nozzles divided by the dpi resolution. The history of ink-ejecting printers includes an evolution of increasing dpi resolution to satisfy ever-increasing resolution and performance demands. Along with this evolution came a history of ever-increasing swath heights. Increasing swath heights are found throughout the printer manufacturing industry and across most printer manufacturing company model lines.
Thus, an ever-increasing swath height is expected. Unfortunately, larger swath heights introduce certain inefficiencies into the printing process. As will be appreciated, printing inefficiencies ultimately result in relatively less overall page throughput. More specifically, a larger swath height pays a greater penalty for xe2x80x9cremainder swathsxe2x80x9d, i.e., where only a partial swath height is needed to complete a given page. A complete print head scan is required, but a complete swath of image is not produced. This results in inefficient use of scan time, i.e., time in which the print head scans across the page.
Smaller swath heights, as in the history of such printers, did not introduce significant inefficiencies due to the relative size of swath height and vertical dimension of a given page. More particularly, previous printing heads had swath heights at only a small percentage of the total needed, i.e., small compared to page length. Hence remainder swaths did not significantly impact page throughput. For example, the above-noted swath heights of ⅙th inch (0.423 cm), ⅓rd inch (0.847 cm) and xc2xd inch (1.27 cm) were small in comparison to the typical 11-inch (27.94 cm) page height. Thus, a relatively large number of print head scans were required for each page because the swath height was much, much smaller than the page height.
As swath height grows, however, the need for an additional swath or print head scan represents a correspondingly more significant portion of the overall page and, therefore, the overall print time required for that page. Thus, inefficient use of print head scan time, i.e., such as resulting from printing using only a portion of swath height, represents a potential for increasing inefficiency as swath heights grow in comparison to the typical page height. Such xe2x80x9cremainder swathsxe2x80x9d occur when an integer multiple of the swath height mismatches page height. Thus, for example if the swath height were equal to the page height then no remainder swath issue arises. Similarly, for an integer multiple of the swath height equal to the page height no remainder swath issue arises. In other words, if an integer multiple of the swath height equals the printing area of the page, then no remainder swaths will occur, i.e., no condition occurs where only a portion of the swath height is used for printing. Unfortunately, users designate different sized media and set margins of varying dimensions. As a result, the actual printing area on a given page varies and does not equal in every case an integer multiple of the swath height. Accordingly, remainder swaths arise as a source of throughput inefficiency.
FIG. 1 (Prior Art) illustrates schematically the relative size relationship between a print head 10 having a xc2xd inch (1.27 cm) swath height 12 and a page 14 having an 11 inch (27.94 cm) page height 16. To cover the entire page 14, print head 10 must scan across page 14 at least 22 times, i.e., xc2xd inch (1.27 cm) vertical coverage for each scan and 22 total scans to cover 11 inches (27.94 cm). In this typical prior art configuration, each swath height 12 corresponds to 4.5% of the page height 16. Thus, an additional scan required at the bottom of a page, but only utilizing a portion of the print head 10 swath height 12, represents at most an inefficiency of nearly 4.5% relative to the overall page 14.
Printer swath heights are increasing and are expected to increase significantly. As swath heights increase, greater inefficiencies will result. For example, swath heights of several inches are foreseeable. Future ink-ejecting printers will likely have even greater swath heights.
FIG. 2 (Prior Art) illustrates significant inefficiency under prior art printing methods as swath heights increase relative to typical page height. In FIG. 2, print head 20 enjoys, for example, a 3.4-inch (7.62 cm) swath height 22. Page 24 has a page height 26 of 11 inches (27.94 cm). To guarantee coverage of the entire page 24, print head 20 must scan at least four times. Thus, under the configuration illustrated in FIG. 2, each scan or swath height 22 represents 25% of the required page 24 printing operation. An inherent and significant inefficiency arises because the relative size of the swath height 22 and page height 26 invariably results in a certain portion of the last print head 20 scan not utilizing a full swath height 22. Thus, for a final scan of page 24 utilizing a very small portion of the swath height 22, a nearly 25% inefficiency in page throughput relative to scan time results.
It would be desirable, therefore, to adapt to ever-increasing swath heights while not suffering the ever-increasing page throughput inefficiencies resulting from increased swath height.
The present invention proposes more efficient use of scan time by coordinating successive media transport to identify a gap or separation between successive media less than the swath height and to print when possible on two consecutive media concurrently during a single print head scan, i.e., when print head swath height spans a gap between successive media.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation of the invention, together with further advantages and objects thereof, may best be understood by reference to the following description taken with the accompanying drawings wherein like reference characters refer to like elements.